Good eyes, I never believe the one size fits all and yes they did use a different piston 12110-30001 with cast rings Part Number 12140-30600 the last 2 digits of suzuki numbers or an additional suffix denote OS. Great engine 1 year only developed for ISDT but they soon had the RM sorted and used that engine in the PE. The following TS models were all reed engines and used chrome rings and steel bores.
When I look up 12110-30001 it shows that number suiting a range of models.
https://www.partzilla.com/product/suzuki/12110-30001There are even oversize versions which don't work in a plated cylinder.
The other possibility is that when it superseded from 12110-30000 they moved the ring pegs out to suit the exrta transfers of the new cylinder and then decided it would be ok in the old ones as well. Or they thought it would work ok with the ring end dropping into the port. There are some of the later pistons on Ebay so we may be able to get them to measure the peg positions.
The owner of the bike bought it as a basket case and doesn't have the original piston to measure but sent the barrel to me to fit a sleeve ne had got from Vintco which is meant to fit all from TS, TM to RL from 73 to 81 but it is nothing like any of the early versions.
